1. Field of the Invention
L-lysine is an important amino acid used as a feed additive for broilers and swine, as examples, because the amount of L-lysine is insufficient in feed crops such as corn. The present invention relates to a improved process for producing L-lysine by fermentation.
2. Discussion of the Background
Previous known conventional methods for producing L-lysine by fermentation comprise imparting properties necessary for acquiring the L-lysine productivity such as homoserrne auxotrophy, S-(2-aminoethyl)-L-cysteine resistance, .alpha.-chlorocaprolactam resistance, for example, to microorganisms belonging to the genus Brevibacterium or the genus Corynebacterium which were isolated from nature (hereafter referred to as wild strains), culturing the microorganisms in a medium containing carbon sources and nitrogen sources, for example, and collecting the L-lysine produced and accumulated in the culture broth by resin adsorption, for example.
Furthermore, a process using improved strains of these L-lysine-producing microorganisms, for example, L-alanine auxotrophs, fluoropyruvate sensitive strains, and L-leucine analog resistant strains, has also been studied but the yield of L-lysine produced by fermentation is not yet satisfactory. Thus, the need exists for the development of a more efficient process for producing L-lysine at lower costs than those previously provided by the conventional processes.
The present invention provides for such a process that efficiently produces L-lysine at lower costs than the previously known processes by enhancing the L-lysine productivity of L-lysine-producing microorganisms or mutants thereof, thereby improving the fermentation yield.